This is an optional Exotek TLR 22-4 Aluminum Rear Hub Set. These heavy duty 7075 rear hubs feature vertical ball stud mounting to allow easy roll center adjustments by adding or removing shims. They includs an extra 3mm hole for using a 3mm set screw (not included) to secure the hinge pin and use the stock 0 degree geometry. The included 1mm spacer for the 22-4 ball ends are designed to match the stock 'B' setting of the plastic hubs for easy set up reference. 'C' setting uses no spacers and 'A' setting requires 2mm spacers (extra 1mm spacer not included).